The Last Story is not only the most possible answer, but is also the one that would benefit the most. It could've used the GamePad's features to deliver its promise of deep tactics along with fast-paced combat. But... I would rather have Mistwalker create a game from the ground up for Wii U and forget about TLS altogether.
Pandora's Tower and Rodea would have to be significantly altered in order for the GamePad to be a reasonable control option, and both games had already been in development for a very long period of time. Earth Seeker is a tough sell because it bombed in Japan to begin with. It could find an audience in the West on the RPG-starved Wii U, but I'm not convinced that it's worth the effort.
I think a Xenoblade HD port for Wii U might be worthwhile. But that's off-topic.
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